JP2004149867A - Gas diffusion electrode and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode which is used for a cathode for oxygen generation in brine electrolysis and used for a fuel cell or the like, is manufactured by a simple operation in a short period of time, and has a gas feed layer and a reaction layer having a uniformly or optionally changing structure, and to provide a manufacturing method therefor. <P>SOLUTION: This manufacturing method is characterized by using a porous body for the gas supply layer or/and the reaction layer, which is obtained by means of electrophoretically precipitating fine particles for forming the gas diffusion electrode, from a dispersion liquid containing the fine particles for forming the gas diffusion electrode, of which the electrophoretic mobility is adjusted, on the surface of a substrate disposed on an electroconductive base material or in the proximity. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas diffusion electrode used for an oxygen cathode for salt electrolysis or a fuel cell, and a method for producing the same, and more specifically, can be produced in a short time with a simple operation, and is uniform or optionally. The present invention relates to a gas diffusion electrode having a gas supply layer and a reaction layer having a changed layer configuration, and a method for manufacturing the same.
[0002]
[Prior art]
The gas diffusion electrode is an oxygen cathode for salt electrolysis or an electrode used for a hydrogen fuel cell. A fuel cell using this gas diffusion electrode holds an oxygen electrode (cathode) for supplying oxygen and an electrolyte. It is composed of three elements, an electrolyte plate and a fuel electrode (anode) to which fuel is supplied. In salt electrolysis, only an oxygen electrode (cathode) for supplying oxygen is used as an oxygen cathode.
[0003]
In particular, a solid polymer electrolyte type fuel cell has a structure in which gas diffusion electrodes are disposed on both sides of an ion exchange membrane (solid polymer electrolyte membrane), and this gas diffusion electrode is fixed in a normal state. The reactant gas supplied with the electrolyte on the surface electrode performs power generation or depolarization while electrochemically reacting, and includes a reaction layer and a gas supply layer.
[0004]
These gas diffusion electrodes are basically composed of a catalyst, carbon black, ethylene tetrafluoride resin (PTFE dispersion) and a current collector, and usually have a thickness of about 0.6 mm. The gas supply layer has a structure of about 5 mm as a gas supply layer and about 0.1 mm as a reaction layer. The gas supply layer contains, for example, hydrophobic carbon black and fine particles of polytetrafluoroethylene (PTFE) as components. The layer is composed of fine particles of catalyst, fine particles of hydrophilic carbon black, hydrophobic carbon black and fine particles of polytetrafluoroethylene (PTFE).
[0005]
Regarding the method of manufacturing these gas diffusion electrodes, the applicant has, for example, proposed a method of applying gas by a simpler method than the method of applying the above-mentioned fine particles in a paste form (for example, see Patent Documents 1, 2, and 3). One proposal was made on a method for manufacturing a diffusion electrode and a reaction layer and a gas supply layer of a gas diffusion electrode which are basic elements of a solid polymer electrolyte fuel cell (see Patent Document 4).
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-102071 (Claims, Claim 4)
[Patent Document 2]
JP 2001-160403 A (Example 1)
[Patent Document 3]
Japanese Patent Application Laid-Open No. 7-134993 (claims)
[Patent Document 4]
International Publication WO01 / 94688 (Claims)
[0007]
[Problems to be solved by the invention]
The invention of this proposal, from a dispersion having a high water content containing fine particles for forming a gas diffusion electrode mainly composed of fluororesin fine particles, has a small water content in a short time, and does not cause a concentration difference due to segregation of the fluororesin, A fluororesin-containing porous body having a uniform concentration distribution, in particular, a cake-like fluororesin-containing porous body is prepared, and a reaction layer or a gas supply layer of a gas diffusion electrode is prepared using the fluororesin-containing porous body. Further, the present invention is excellent in that a gas diffusion electrode having high performance and long life can be manufactured by an easy manufacturing method and at low cost.
[0008]
In addition, the invention of this proposal provides a solid polymer electrolyte membrane which is excellent in mass productivity, can be manufactured at a low cost with a simple device, and has a high performance and a long life. A cathode and an anode are immersed in an electrophoretic solution composed of a solution of a solid polymer electrolyte (hereinafter, referred to as a solution) such as (manufactured by DuPont), and an electric current is applied so that the solid polymer electrolyte is electrophoresed on the anode side. It is an excellent material that can be prepared by electrodeposition on a substrate placed on or near the anode, specifically on a porous body.
[0009]
However, the inventors have keenly sought a method capable of preparing a gas diffusion electrode more easily and in a shorter time, and capable of forming a gas supply layer and / or a reaction layer having a uniform thickness. As a result of the examination, the fine particles dispersed in the dispersion liquid containing the fine particles for forming the gas diffusion electrode mainly composed of the fluororesin fine particles were electrophoresed, and the electrophoresis was performed on the porous body (substrate) placed on or near the anode. It has been found that the electrokinetic potential (zeta potential; ζ potential) of the dispersed fine particles is an important factor in determining the electrophoretic speed, as well as the electric conductivity of the dispersion liquid during the deposition.
[0010]
Further, the electrophoresis speed has a great influence on the electrodeposition characteristics, and further on the obtained reaction layer of the gas diffusion electrode and the characteristics of the gas supply layer, and the components constituting the gas supply layer and the reaction layer forming the gas diffusion electrode. By changing the electrophoresis speed, more specifically, changing uniformly or arbitrarily in each layer, and distributing those components, the characteristics of the reaction layer and the gas supply layer of the gas diffusion electrode are changed. They found that they could be changed and completed this invention.
[0011]
[Means for Solving the Problems]
That is, the invention described in claim 1 of the present invention
From the dispersion containing the fine particles for forming the gas diffusion electrode whose electrophoresis speed has been adjusted, the fine particles for forming the gas diffusion electrode are electrophoretically deposited on the surface of the conductive substrate or the substrate disposed near the conductive substrate. Using the porous body obtained by the above as a gas supply layer and / or a reaction layer
A method for manufacturing a gas diffusion electrode, characterized by the following.
[0012]
The invention described in claim 2 of the present invention
The method for producing a gas diffusion electrode according to claim 1,
The gas diffusion electrode forming fine particles,
Must consist of fluororesin fine particles and carbon black fine particles
It is characterized by the following.
[0013]
Further, the invention described in claim 3 of the present invention is:
The method for producing a gas diffusion electrode according to claim 1,
The gas diffusion electrode forming fine particles,
It is composed of one or more kinds of fine particles selected from fluororesin fine particles, carbon black fine particles, polymer electrolyte fine particles, metal colloid, metal fine particles and metal oxide fine particles.
It is characterized by the following.
[0014]
Further, the invention described in claim 4 of the present invention is:
The method for producing a gas diffusion electrode according to claim 3,
The metal fine particles and metal oxide fine particles,
Being carried on carbon black
It is characterized by the following.
[0015]
Further, the invention according to claim 5 of the present invention provides:
The method for producing a gas diffusion electrode according to any one of claims 2 to 4,
The fluororesin fine particles and carbon black fine particles,
Differently adjusting the electrophoresis speed in the dispersion
It is characterized by the following.
[0016]
Further, the invention described in claim 6 of the present invention is:
The method for producing a gas diffusion electrode according to any one of claims 1 to 5,
Adjustment of the electrophoresis speed,
It is performed by changing the zeta potential of the fine particles.
[0017]
Furthermore, the invention described in claim 7 of the present invention
The method for producing a gas diffusion electrode according to claim 6,
The change in the zeta potential is:
To be performed by adjusting the type of surfactant, its concentration and pH in the fine particle dispersion, or adding an ion dissociable compound to the fine particle dispersion.
It is characterized by the following.
[0018]
Furthermore, the invention according to claim 8 of the present invention provides:
A gas diffusion electrode prepared by the method for manufacturing a gas diffusion electrode according to claim 1.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a fluororesin-containing porous material formed by depositing a gas diffusion electrode material by electrophoresis from a dispersion containing fine particles for forming a gas diffusion electrode mainly composed of fluororesin fine particles on the surface of a conductive substrate. The present invention relates to a method for producing a gas diffusion electrode using a porous body for a gas supply layer and / or a reaction layer of an electrode, and has the greatest feature that the electrophoresis speed of fine particles for forming a gas diffusion electrode is adjusted. .
[0020]
The dispersion containing the material for forming a gas diffusion electrode mainly composed of fluororesin fine particles is, for example, in the case of a dispersion for forming a gas supply layer, a hydrophobic carbon black is stirred and dispersed in water containing a surfactant. Then, a dispersion operation is performed by a jet mill to obtain a particle diameter of 1 micron or less, and a dispersion liquid of fine fluororesin particles such as PTFE dispersion is added thereto, and the mixture is prepared by stirring and mixing. In order to make the electric conductivity low and constant, it is preferable to use dialysis or ultrafiltration.
[0021]
Also, when preparing a gas diffusion electrode for a solid polymer electrolyte type fuel cell, for example, fine particles of a solid polymer electrolyte (fluorine-based ion exchange resin: Nafion manufactured by DuPont) are mixed with the dispersion liquid. Thereby, the adhesion between the reaction layer and the solid polymer electrolyte membrane is improved.
[0022]
Furthermore, if the dispersion liquid contains a large amount of water contained in the obtained fluororesin-containing porous material, it may flow out of the anode, so that the water content in the porous body formed by electrodeposition is reduced. A water content reducing agent such as glycine, triethanolamine, laurylpyridinium chloride, pyrogallol, or butyltriethanolamine is added as an additive in the range of 0.1 to 2 mmol / l.
[0023]
As such fluororesin fine particles, fine particles of ethylene tetrafluoride resin, ethylene tetrafluoride / hexafluoropropylene copolymer, ethylene trifluoride chloride resin and perfluoroalkoxy resin are used.
[0024]
In the case of a dispersion liquid for forming a reaction layer, in addition to hydrophobic carbon black, hydrophilic carbon black, catalyst fine particles and the like are used in combination, but the catalyst and the hydrophilic carbon black are separately prepared. Not only fine particles of the above, but also those in which a catalyst is attached and integrated on hydrophilic carbon black are used.
[0025]
The same fluororesin fine particles as described above are used, and as the catalyst, fine particles or colloids of a metal selected from gold, silver or platinum group metals and their alloys or oxides thereof are used.
[0026]
The fine particles dispersed in these liquids, including the fluororesin fine particles, have a particle diameter of about 0.1 to several tens of μm and are in a colloidal state or a state close to the colloidal state. It has a kinetic potential (zeta potential).
[0027]
In the present invention, the zeta potential of the fine particles is adjusted by a method of dispersing the fine particles, adjusting the pH of the dispersion, adding an ion-dissociating compound, and the like, and as a result, the respective electrophoretic velocities can be adjusted to desired values. After that, the particles are subjected to electrophoresis to deposit those fine particles on the surface of the conductive substrate or the substrate disposed near the conductive substrate, thereby forming a porous body used as a gas supply layer or / and a reaction layer. What you get.
[0028]
The method of adjusting the zeta potential, the method of dispersing the fine particles, the adjustment of the pH of the dispersion, the addition of the ion dissociable compound, and the like are specifically performed as follows.
[0029]
<Dispersion method of fine particles>
For dispersion of the fine particles, a polyoxyethylene type nonionic surfactant is desirable as a surfactant, and ion exchange water containing about 1 to 8% of this surfactant is used. In some cases, ultrapure water is used. If the conductivity of the surfactant-containing water is greater than 50 μS / cm, the water is deionized through the ion exchange resin layer.
[0030]
In order to disperse the carbon black in the surfactant-containing water, an ultrasonic homogenizer, a jet mill, or the like is used. In particular, use in a jet mill is desirable because the particle size becomes uniform. 1000-2000kg / cm when dispersed by jet mill²The particles are dispersed by passing through at least three times.
[0031]
After dispersing the carbon black, a PTFE dispersion is added and mixed with stirring to form a gas supply layer dispersion. The reaction layer dispersion is prepared in the same manner. At this time, the ratio of the zeta potential between carbon black and PTFE fine particles increases as the surfactant concentration increases, so that the carbon black concentration is high at the beginning of electrodeposition and becomes low when the electrodeposition is completed. And / or the concentration gradient in the porous body used as the reaction layer can be increased.
[0032]
<PH adjustment of dispersion>
The pH can be adjusted with ordinary acids and alkalis, but ammonia is particularly desirable when making it alkaline, and organic acids and carbonic acids are desirable when making it acidic. The zeta potential does not change so much from pH 4 to 10, but if the pH is made acidic at about pH 2, the negative value of the zeta potential becomes 0 or positive. If the pH greatly deviates from 7, the conductivity becomes too large. Therefore, in the case of electrodeposition, it is desirable to be near neutral.
[0033]
<Surfactant>
Examples of polyoxyethylene surfactants include many surfactant manufacturers, including Triton (Triton X100) manufactured by Union Carbide, for example, Kao, Lion, Nippon Yushi, Nikko Chemicals, Nippon Emulsifier, Daiichi Kogyo Pharmaceutical And those commercially available from Sanyo Chemical Industries, Ltd., and particularly, a surfactant having an HLB of about 13.5 is preferably used.
[0034]
Specifically, in addition to Triton X100, for example, Newcol 1310 of Nippon Emulsifier, NL-90 of Daiichi Kogyo Seiyaku, Dispanol TOC of Nippon Oil & Fat, BT-9 of Nikko Chemicals, LS-110 of Kao, Leocol SC of Lion -90 and the like.
[0035]
Among them, surfactants having a conductivity of 100 μS / cm or more when made into a 5% aqueous solution are not suitable for electrophoretic electrodeposition. To adjust the conductivity, it may be possible to use the resin by passing the ionic resin and removing the ionic substance. The zeta potential becomes more negative by ion exchange.
[0036]
It is important to specify the type of surfactant. For example, even at the same surfactant concentration, different zeta potentials are given depending on the type of surfactant. In the dispersion of carbon black, the negative values of the zeta potential are in descending order,
New Coal 1310> Dispanol TOC> Triton X100
Becomes
[0037]
<Type of PTFE dispersion>
Commercially available PTFE dispersions include XAD911 manufactured by Asahi Glass, 30-J manufactured by Mitsui Fluorochemicals, and D-1 manufactured by Daikin Industries. The zeta potential in the same surfactant is negative. In the order of the value of
XAD911> 30-J> D-1
It is.
[0038]
By changing the type of this surfactant, its concentration and the type of PTFE dispersion, the above-mentioned PTFE concentration can be inclined. The combination of Newcol 1310 and XAD911 has a small PTFE concentration gradient, and Triton X100 and D The combination of -1 has a large slope of the PTFE concentration.
In addition, carbon black No. of 4% Newcol 1310 aqueous solution was used. The zeta potential of No. 6 is -22.0 mV, and that of XAD911 is -17.3 mV. The electrodeposit from this dispersion had a small slope of the PTFE concentration.
[0039]
<Addition of ion dissociable compound>
Addition of an ion-dissociating compound such as glycine, aminophenol, or quaternary ammonium salt changes the zeta potential.
[0040]
In particular, carbon black and PTFE fine particles have different effects on the zeta potential.
For example, the zeta potential in a 4% Triton X100 solution is determined by the carbon black No. Although 6 = -30.0 mV and D-1 = -3.6 mV, when 0.1% of glycine is added, they become -29.0 mV and -0.68 mV, respectively.
[0041]
Therefore, when the glycine-added dispersion is electrodeposited, the gradient of the PTFE concentration becomes larger. When 0.05% of p-aminophenol is added, carbon black no. 6 = -40.0 mV, which is a more negative value, but the zeta potential of the PTFE fine particles hardly changes. Further, these additives have a large effect of reducing the water content of the electrodeposit.
[0042]
The zeta potential can be controlled with an anionic surfactant or a cationic surfactant. For example, when 0.01% of Kao's Poise 520, which is an anionic surfactant, is added to a 4% aqueous solution of Newcol 1310, carbon black no. The zeta potential of No. 6 is -36.8 V, and that of XAD911 is -17.4 mV, which are larger negative values.
[0043]
The method for manufacturing a gas diffusion electrode of the present invention comprises, as basic components, a DC stabilized power supply, a porous counter electrode placed in parallel, a dispersion of a gas diffusion electrode material mainly composed of silver mesh and fluororesin fine particles. Things.
[0044]
Specifically, after a silver mesh is laid on the bottom of a cylindrical container to form an anode, the container is filled with a dispersion, and a nickel mesh is placed slightly below the liquid surface of the dispersion in parallel with the silver mesh. This is performed using an electrophoresis tank serving as a cathode.
[0045]
In the electrophoresis, in theory, the anode and the cathode can be performed in any state arranged horizontally or vertically, but hydrophobic carbon black or hydrophilic carbon black dispersed in a dispersion liquid can be used. The anode and cathode are placed horizontally, and the anode to which the gas diffusion electrode material is attached is placed below the anode so that the direction in which the fine particles of fluororesin moves by electrophoresis and the direction of sedimentation due to gravity are the same. It is arranged in.
[0046]
Hereinafter, in this description, a method of depositing and adhering the gas diffusion electrode material to the anode will be described. However, by disposing the anode and the cathode as described above, the moving time of the gas diffusion electrode material can be shortened, and the efficiency can be reduced. In addition to this, the gas diffusion electrode material can be uniformly attached to the anode which is the conductive base material, and the composition can be made equal.
[0047]
In electrophoresis, the anode does not necessarily need to be fixed, and if the anode is continuously moved, a porous body to which the gas diffusion electrode material is uniformly attached can be continuously manufactured. Preferably, a porous body is continuously produced by using a metal mesh as an anode serving as a base of the porous body and moving the same continuously.
[0048]
The material of the anode may be any metal such as noble metals, silver, copper, zinc, iron, aluminum, nickel, stainless steel, and alloys thereof, and carbon. The same applies to the cathode, and the gap between the electrodes is preferably 5 to 100 mm. However, if it is too close, there is a risk of short circuit, and if it is wide, a high voltage power supply is required.
[0049]
When metals such as zinc, copper, iron, aluminum, and nickel are used as the material of the anode, the electrodeposits contain about 0.01 to 2% of these metals. However, if their presence is a problem, it is preferable to use carbon, platinum, gold, palladium, or the like as the anode.
[0050]
When a carbon plate is used as the material of the anode, the electrodeposited surface is consumed by an oxidation reaction. Therefore, it is preferable that the surface is plated with a metal such as zinc before use.
[0051]
The shape of the metal used as the anode is preferably a net shape, but may be a plate shape. In the case of a net shape, a mesh having a mesh size of about 0.5 to 2 mm is preferable. However, it may be in the form of a plate, and is preferably in the form of a net, because the generated hydrogen bubbles are easily removed. Further, a gas diffusion electrode can be used.
[0052]
In order to reinforce the electrode, a fibrous substance can be adhered to the surface of the anode and electrodeposited, so that the fibrous substance can be included in the porous body. In addition, by installing a filter (filter paper) in close contact with the surface of the anode, the gas diffusion electrode material can be deposited on the upper part of the filter, and the anode and the porous body obtained by the deposition can be easily separated. Can be.
[0053]
Further, when a diaphragm is provided between the anode and the cathode, and the anode chamber and the cathode chamber are separately installed, OH generated along with generation of hydrogen at the cathode is generated.⁻Due to the ions, the dispersion liquid becomes alkaline, the electrical conductivity increases, the current becomes excessive, the electrodeposition does not proceed, the current flows, the liquid temperature rises, and the electrodeposition is adversely affected. Can be prevented.
[0054]
That is, when the electrodeposition tank is separated into an anode chamber and a cathode chamber by a diaphragm, the OH generated at the cathode is reduced.⁻Prevents the migration of ions to the anode compartment, prevents the increase in the electrical conductivity of the dispersion, reduces the pH change of the dispersion, reduces the contamination of the cathode, and uses porous membranes and ion exchange membranes as diaphragms. As the ion exchange membrane, a cation exchange membrane, a composite membrane of a cation exchange membrane and a carboxylic acid membrane, or the like can be used.
[0055]
A direct current voltage of 5 to 300 V is applied between the anode and the cathode, a current of about 10 to 200 mA is applied, and a current of about 20 to 60 minutes is applied. Precipitates out. The deposition rate is 90-99% or more.
[0056]
As the power source, a DC constant voltage, a DC constant current, a DC pulse current, or the like is used, and it can be used properly according to the purpose such as making the concentration of the fluororesin in the porous body uniform or giving the concentration a gradient.
[0057]
Although electrophoresis can be performed at room temperature, it is preferable. For example, when electrophoresis is performed using a dispersion having a high voltage, a low concentration of fine particles, and a high electrical conductivity, the temperature of the dispersion may increase due to Joule heat.
[0058]
Further, when electrophoresis is performed with a dispersion liquid having a temperature exceeding 30 ° C., the solvent (water) present in the obtained fluororesin-containing porous material becomes 50% or more, and the fluororesin-containing porous material In the electrophoresis, the dispersion does not exceed a temperature of 30 ° C., and preferably has a temperature of 20 ° C. It is good to control while controlling the liquid temperature so as not to exceed.
[0059]
The obtained fluororesin-containing porous body, in particular, a cake-like fluororesin-containing porous body is dried, and then added with solvent naphtha and rolled to form a sheet, thereby forming a reaction layer for a gas diffusion electrode or a gas supply layer. Sheet.
[0060]
When preparing a gas diffusion electrode using the gas supply layer thus obtained, in order to impart long-term stability to the gas diffusion electrode, a fluororesin water-repellent layer is formed on the entire surface of the gas supply layer with a diameter of 1 mm. It is preferable to provide a point-like or partially strip-like shape.
[0061]
When the water content of the obtained fluororesin-containing porous body is about 50%, when the fluororesin-containing porous body is dried, cracks may be generated due to shrinkage. Even if it can be eliminated from the appearance, the strength of the cracked part is slightly lower than others.In such a case, the crack is applied by pressing the electrode in the thickness direction more than the contraction force when drying. It is desirable to prevent.
[0062]
Further, since drying takes more than one day at room temperature, it is preferable to dry quickly by raising the temperature and increasing the water vapor pressure during drying. However, the drying temperature is preferably 200 ° C. or lower.
[0063]
At that time, if the drying temperature is too high, decomposition may occur in a system containing a surfactant, and if the solvent is alcohol or the like, the vapor pressure is too high and evaporates explosively, so the electrodes may be destroyed. Therefore, in order to prevent them, the surface of the porous body containing the fluororesin fine particles is sandwiched between porous films, and further sandwiched between the porous bodies under which gas can move sufficiently under pressure, and then the solvent is removed under pressure and heating. A removal method is employed.
[0064]
Hereinafter, an example of a method for manufacturing a solid polymer electrolyte fuel cell including the gas diffusion electrode of the present invention will be schematically described.
[0065]
<Step 1>
Using a stainless steel foil or the like as an anode, a gas supply layer (electrophoresis using a dispersion liquid containing fluorocarbon resin particles in which hydrophobic carbon black particles are dispersed) and a reaction layer (hydrophobic carbon black, hydrophilic carbon black, Electrophoresis using a dispersion or solution of a fluororesin dispersed with a catalyst, metal fine particles or metal oxide fine particles) and a solid polymer electrolyte membrane (electrophoresis using a polymer electrolyte solution) by electrophoresis, The two stainless steel foils on which the obtained gas supply layer, reaction layer, and solid polymer electrolyte membrane were laminated were heated and pressed with the laminated body in the middle at the time of fresh drying, and then the outer stainless steel foil was peeled off. Used.
[0066]
<Step 2>
In the same manner as in Step 1, a reaction layer and a solid polymer electrolyte membrane obtained by electrodepositing a reaction layer and a solid polymer electrolyte membrane on a stainless steel foil by electrophoresis, and water-repellent carbon Paper or the like is used as the gas supply layer.
[0067]
<Step 3>
In the same manner as in the step 1, a reaction layer and a gas supply layer were sequentially formed on the stainless steel foil by electrodeposition by electrophoresis. At the time of raw drying, the solid polymer electrolyte membrane is heated and pressed and joined, and then the outer stainless steel foil is peeled off.
In this case, in preparing the reaction layer by electrophoresis, it is preferable to use a solution of a solid polymer electrolyte in combination with the electrophoresis liquid, whereby the adhesion between the reaction layer and the solid polymer electrolyte membrane can be improved.
[0068]
<Step 4>
In the electrophoresis tank, a solid polymer electrolyte membrane is provided between the anode and the cathode, and fine particles moving by electrophoresis are attached to the solid polymer electrolyte membrane to form a reaction layer and a gas supply layer on the membrane. Let it.
[0069]
<Step 5>
In the same manner as in Step 1, a reaction layer, a solid polymer electrolyte membrane, and a laminate of a reaction layer / solid polymer electrolyte membrane / reaction layer obtained by electrodepositing the reaction layer by electrophoresis sequentially on a stainless steel foil Water-repellent carbon paper or the like is used as the gas supply layer.
[0070]
<Step 6>
In the same manner as in Step 1, a gas supply layer, a reaction layer, a solid polymer electrolyte membrane, a reaction layer, and a gas supply layer are sequentially electrodeposited on a stainless steel foil by electrophoresis to form a gas supply layer / reaction layer / solid height. Used as a laminate of molecular electrolyte membrane / reaction layer / gas supply layer.
[0071]
In addition, the said manufacturing method is only an example, and the preparation method is not limited to the said method, As mentioned above, the reaction layer and / or gas supply layer formed by electrophoresis are dried, and solvent naphtha etc. In addition, it can be rolled to form a sheet and used as a reaction layer and / or gas supply layer sheet. When the formed reaction layer and gas supply layer are heated and pressed at the time of fresh drying, a porous plate is formed on a press plate, etc. It is similarly possible and preferable to use a body or to provide a water-repellent layer made of a fluororesin on the entire surface of the gas supply layer in the form of a dot having a diameter of about 1 mm or a partial band.
[0072]
In the present invention, the dispersion liquid containing fine particles of the fluororesin as described above, for example, a PTFE dispersion or the like uses water as a dispersion medium, and the fine particles of the fluororesin dispersed in water. Hydrophobic carbon black and hydrophilic carbon black dispersed in a dispersion liquid containing fine particles also usually have negative ions and have a zeta potential.Thus, by attaching these fine particles to the anode by electrophoresis, Thus, a fluororesin-containing porous body serving as a gas supply layer and / or a reaction layer of the gas diffusion electrode is prepared.
[0073]
At that time, the zeta potential of the fine particles may be different for each particle, and the fine particles having different zeta potentials, at the same voltage, have different speeds at which they move to the electrodes, so-called electrophoretic speeds, and a dispersion of the fine particles. Even if the component ratio in the inside is specified, particles having a large zeta potential move to the electrode surface at a high speed and precipitate, so that the component ratio of the precipitate differs from the component ratio in the dispersion.
[0074]
Therefore, as for the components, even when the dispersions having the same composition are used, the formed precipitates, that is, the components of the fluororesin-containing porous body are different from each other, so that the one having different characteristics may be obtained.
For this purpose, in the present invention, the zeta potential in the dispersion liquid of the gas diffusion electrode forming fine particles is adjusted.
[0075]
If the zeta potential in the dispersion liquid of the gas diffusion electrode forming fine particles is adjusted to be equal to the zeta potential in the dispersion liquid of the fluororesin fine particles and the carbon black fine particles, the obtained fluororesin-containing porous body is componentally It is formed from a uniform layer.
[0076]
In addition, when it is desired to particularly impart properties to the fluororesin-containing porous body, for example, when it is desired to make a difference in hydrophobicity between the front surface and the bottom surface, by varying the zeta potential of the fluororesin fine particles or carbon black fine particles. On the bottom side, the ratio of fine particles having a high zeta potential can be increased, and on the surface side, the ratio of fine particles having a low zeta potential can be increased, so that a fluororesin-containing porous body having specific properties can be obtained. .
[0077]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
Example 1
At the bottom of the container, a silver mesh serving as a base of the gas diffusion electrode was provided as an anode, and a silver mesh cathode was provided in parallel with the anode at a distance of 1 cm upward therefrom to form an electrophoresis tank.
19.5 g of hydrophobic carbon black was added to 300 ml of distilled water containing 4% of Triton, and dispersed in a jet mill to 1 μm or less. The zeta potential of the hydrophobic carbon black in this dispersion was -31 mV.
On the other hand, a PTFE dispersion (D-1, manufactured by Daikin Industries, Ltd.) having a zeta potential of −15 mV in distilled water containing 4% of Triton was prepared, 14.7 ml of the dispersion was added to the carbon black dispersion, and a gas supply layer was formed. This was a dispersion for formation. This dispersion is placed in the above-mentioned electrophoresis tank, and a DC voltage of 30 V is applied between the anode and the cathode from a DC stabilizing power supply for 45 seconds. A fluororesin-containing porous body usable as a gas supply layer for the electrode was obtained.
In this fluororesin-containing porous body, the fluororesin concentration continuously changes from 24.5% at the electrodeposition initial portion to 42.5% at the end portion in the depth direction of the electrode. Was.
[0078]
Example 2
A gas supply layer was prepared in the same manner as in Example 1 except that the type of the surfactant was Newcol. In a 4% aqueous solution of Newcol 1310, carbon black No. Dispersion of No. 6 gave a zeta potential of -22.0 mV, and similarly, a PTFE version XAD911 of -17.3 mV.
The electrodeposit from this dispersion had a small slope of the PTFE concentration. The fluororesin-containing porous body has a fluororesin concentration continuously varying from 34.5% at the electrodeposition initial portion to 39.6% at the end portion in the depth direction of the electrode. Met.
[0079]
Example 3
In 1000 ml of a 4% Triton solution, carbon black No. 6 and add 100 kg with a jet mill.²For 5 times to obtain a dispersion having an average particle size of 390 nm. The zeta potential showed -30.0 mV. In a 4% Triton solution, PTFE disversion D-1 exhibited a zeta potential of -3.6 mV.
When 0.1% glycine was added to these liquids, No. 1 was obtained. 6 was -29.0 mV, and D-1 was -0.68 mV.
D-1 was added to the carbon black dispersion to a concentration of 40%, followed by stirring and mixing. Electrodeposition was performed in the same manner as in Example 1 using this gas supply layer dispersion.
The obtained fluororesin-containing porous body has a fluororesin concentration continuously changing as 18.9% at the electrodeposition initial portion and 56.8% at the end portion in the depth direction of the electrode. Met.
[0080]
【The invention's effect】
The gas diffusion electrode of the present invention includes, for example, a solvent naphtha formed on a fluororesin-containing porous body in which a gas diffusion electrode material mainly composed of fluororesin fine particles is uniformly dispersed and formed on the surface of a conductive substrate. The sheet obtained by the addition is used as a gas supply layer or a reaction layer, and it is possible to easily and quickly prepare a gas diffusion electrode having improved performance and life.
[0081]
In the present invention, the equipment configuration for manufacturing the gas diffusion electrode can be simplified, so that the equipment cost can be reduced, the operation cost can be reduced because almost no current flows between the electrodes, and the equal electric field can be applied between the electrodes. Is formed, it is possible to form a gas supply layer and / or a reaction layer having a uniform thickness.
[0082]
Since the gas diffusion electrode material can be quickly attached to the surface of the conductive substrate by electrophoresis, the gas supply layer and / or the reaction layer can be formed in a short time, and the current collector can be continuously formed. Since the gas supply layer and / or the reaction layer can be formed by attaching fine particles to the surface of the metal net, effects such as excellent mass productivity can be obtained.
[0083]
The electric conductivity of the dispersion can be adjusted without precipitating the fluororesin fine particles from the dispersion or destroying the dispersion. A large power supply is required, causing a significant rise in the liquid temperature due to Joule heat, and the oxidation reaction occurs violently at the anode, dissolving the silver mesh of the anode, mixing a large amount of silver ions into the dispersion, and aggregating the dispersion. Such a problem does not occur, and furthermore, by making the electric conductivity constant, the amount of electrodeposition is made constant, and the film thickness of the obtained porous body containing fluororesin fine particles can be made constant.
[0084]
In particular, in the present invention, since the zeta potential in the dispersion liquid of the gas diffusion electrode forming fine particles including the fluororesin fine particles is adjusted, the ratio of the components constituting the obtained fluororesin-containing porous body is made uniform. Or, it is easy to have a slope, so it is easy to keep the quality of the gas diffusion electrode constant, and by giving the slope, it is possible to impart specific performance to the gas diffusion electrode. You can.
[0085]
Further, according to the production method of the present invention, the obtained gas supply layer sheet or reaction layer sheet is dried without cracking, and does not peel off in a subsequent step, and has a strength after hot pressing. And a long-life gas diffusion electrode without unevenness.
[0086]
In addition, because of the electrophoresis, almost no current flows between the two electrodes, so that power consumption is low and a uniform electric field is formed between the two electrodes. A film, a reaction layer or a gas supply layer can be formed, and the fine particles of the gas diffusion electrode material adhere to the electrode surface by the electric force, so-called Coulomb force. Alternatively, there is an effect that a reaction layer can be formed.
[0087]
Therefore, the present invention can be widely used in various industrial fields as a fuel cell or a salt electrolysis electrode.

Claims (8)

From the dispersion containing the fine particles for forming the gas diffusion electrode whose electrophoresis speed has been adjusted, the fine particles for forming the gas diffusion electrode are electrophoretically deposited on the surface of the conductive substrate or the substrate disposed near the conductive substrate. A method for producing a gas diffusion electrode, comprising using a porous body obtained by the above as a gas supply layer and / or a reaction layer. The gas diffusion electrode forming fine particles,
2. The method for producing a gas diffusion electrode according to claim 1, wherein the gas diffusion electrode is made of fluororesin fine particles and carbon black fine particles. The gas diffusion electrode forming fine particles,
2. The composition according to claim 1, comprising one or more kinds of fine particles selected from fluororesin fine particles, carbon black fine particles, polymer electrolyte fine particles, metal colloid, metal fine particles and metal oxide fine particles. A method for producing a gas diffusion electrode. The metal fine particles and metal oxide fine particles,
The method for producing a gas diffusion electrode according to claim 3, wherein the gas diffusion electrode is supported on carbon black. The fluororesin fine particles and carbon black fine particles,
The method for producing a gas diffusion electrode according to any one of claims 2 to 4, wherein the electrophoresis speed in the dispersion is adjusted to be different. Adjustment of the electrophoresis speed,
The method for producing a gas diffusion electrode according to claim 1, wherein the method is performed by changing the zeta potential of the fine particles. The change in the zeta potential is:
The method for producing a gas diffusion electrode according to claim 6, wherein the method is carried out by adjusting the type and concentration of a surfactant in the fine particle dispersion, adjusting the pH, or adding an ion-dissociable compound to the fine particle dispersion. A gas diffusion electrode prepared by the method for manufacturing a gas diffusion electrode according to claim 1.